Modified formula for predicting the maximum wave force on seabed objects

Abstract

A modified wave-force formula, which predicts the maximum horizontal wave force on seabed objects, was developed using the velocity semi-amplitude, defined as half the difference between successive negative (offshore) and positive (onshore) peaks in the near-bed wave orbital velocity, and the corresponding peak-to-peak period. The formula was tested by analyzing wave-force data from three differently shaped structure models under random wave conditions and comparing its prediction accuracies with those of the Morison equation and the conventional wave-force formula based on the positive peak velocity. The maximum forces for individual zero-down-crossing velocity waveforms were predicted by applying each of the respective formulas with force coefficient(s) empirically pre-determined as a function of the Keulegan—Carpenter number. For all wave conditions and model structures, the modified formula was more accurate than the Morison equation, whereas the conventional formula was less accurate. Although the absolute relative prediction error increased as the velocity skewness deviated from 0.5, the increase in the error was least pronounced for the modified formula. The results also demonstrated that the highest maximum wave forces in random wave trains can be predicted with reasonable accuracy by the proposed formula using the highest value of the velocity semi-amplitude and the corresponding period.